Abstract
Background:
Feline herpesvirus type 1 (FHV-1) is a major cause of feline upper respiratory tract disease (FURTD), but its molecular epidemiology and bacterial co-detections remain poorly characterized in Vietnam.

Aim:
To determine FHV-1 PCR positivity among cats with FURTD-compatible signs and evaluate associated factors, partial glycoprotein B (gB) sequences, phylogenetic relationships, and selected culturable bacterial co-detections.

Methods:
This cross-sectional, clinic-based study was conducted during 2025 at the Veterinary Teaching Clinic, Can Tho University, Vietnam. Among 1,177 clinically diseased cats examined, 297 with FURTD-compatible signs underwent conventional PCR targeting partial gB. All enrolled cats were sampled once, and demographic and management variables were recorded at examination. Four representative amplicons were bidirectionally Sanger-sequenced. Selected culturable bacteria were investigated by culture followed by genus- or species-specific PCR. Epidemiological associations were evaluated using univariable logistic regression, while exploratory clinical sign-count scores were compared using the Wilcoxon rank-sum test.

Results:
FHV-1 DNA was detected in 39/297 suspected cases (13.13%), representing 3.31% of all 1,177 clinically diseased cats. Cats aged ≤12 months had greater odds of PCR positivity than older cats (OR = 4.03; 95% CI: 1.88–8.61; p < 0.001), as did outdoor versus indoor cats (OR = 2.60; 95% CI: 1.11–6.12; p = 0.028). The four partial gB sequences shared 99.9%–100% nucleotide identity and 100% deduced amino acid identity. Selected bacterial taxa were co-detected in 24/39 FHV-1-positive cats (61.54%). Cats with bacterial co-detection had higher clinical sign-count scores than those without co-detection (median [IQR]: 3 [2–3] vs. 2 [1–2]; p < 0.001).

Conclusion:
These findings provide baseline clinic-based molecular epidemiological data for FHV-1 in cats from Vietnam’s Mekong Delta. Young age and outdoor access were associated with FHV-1 PCR positivity, and partial gB was highly conserved. Bacterial co-detection was common and associated with higher clinical sign-count scores, although causality cannot be inferred from this cross-sectional study. Because testing was symptom-directed, the 3.31% value should not be interpreted as population prevalence.

Key words: Bacterial co-detection; Can Tho City; Cats; Feline herpesvirus type 1; Molecular epidemiology.